Jim and his friend _____ at this school.[ ]
A. is
B. isn't
C. can't
D. are
答案：D
判断，正确的填A，错误的填B。
南宋时，纸币取代铜钱，成为主要流通货币。
对煤气管道有严重腐蚀的物质是（）
A、苯
B、萘
C、氨
D、甲烷
